The TGF- pathway potently regulates tumor initiation, progression and metastasis. Work supported by this grant over the current funding period has shown that impairment of TGF- signaling, when combined with oncogene activation or tumor suppressor gene attenuation, accelerates the development of carcinomas and enhances tumor progression, including metastasis. Mechanistic studies utilizing the mammary gland models, MMTV-PyMT and MMTV- c-neu, have shown that a major mechanism whereby loss or attenuation of TGF- signaling accelerates tumor progression is increased secretion of cytokines and chemokines by . In the mouse models increased chemokine expression resulted in recruitment of myeloid/immune cells with resultant enhancement of invasion and metastasis. We now have another model in which a single genetic alteration results in a 4-5 fold increase in lung metastases with different mechanisms. The following three hypotheses will be tested in the proposed studies: 1) A major function of TGF- signaling is the suppression of chemokine and cytokine expression, and attenuation or loss of TGF- signaling in carcinoma cells leads to increased secretion of different chemokines and cytokines that play different roles in enhancing metastasis. 2) A mechanism of myeloid/immune cell enhancement of tumor invasion and metastasis is through secretion of TGF-, which induces lysyl oxidase (LOX) that cross-links collagen increasing matrix stiffness and enhancing invasion. 3) The gene expression signature and patterns of expression of selected chemokines and cytokines in tissue microarrays (TMA) of impaired TGF- signaling in our models will predict for worse outcome when applied to publically available human breast cancer datasets. The following specific aims are proposed to test these hypotheses: 1) Determine the mechanism of enhancement of c-neu-induced tumor metastasis by a dominant negative type II TGF- receptor (DNIIR); 2) determine the mechanism(s) of myeloid/immune cell promotion of tumor invasion and metastasis in the PyMT model with conditional knockout of the type II TGF- receptor and in the c-neu/DNIIR model; and 3) Determine whether mechanisms identified in the mouse models are applicable to human breast cancer. PUBLIC HEALTH RELEVANCE: TGF- signaling is a major tumor suppressor pathway in human carcinomas, but in later stages of tumor progression, TGF- signaling promotes tumor progression. As systemic inhibitors of TGF- signaling are in clinical trials in humans with cancer, it is important to delineate mechanisms of both suppression and promotion of tumors by TGF-. We have excellent mouse models and plans for such mechanistic studies.